Numerous systems and apparatuses have been developed for the purpose of preparing and dispensing hot beverages having a smooth and thick froth topping layer of foamed coffee or frothed milk. Such dispensing machines typically operate by combining appropriate amounts of product concentrates like, for instance, instant coffee and milk powders or liquid concentrates with hot water and vigorously mixing them together in a suitable mixing bowl or whipper, and dispensing the reconstituted beverage into a cup or any other container through a dispensing nozzle. Such methods and systems are convenient for producing frothed beverages but the froth as resulting from such methods and systems suffer from several drawbacks.
Particularly, one drawback with the existing automated dispensing devices is that the appearance and consistency of the foam produced are not satisfying. In general, the froth on top of the beverage lacks uniform character, with a wide size range of bubbles and a large number of large bubbles. As a result, the froth shows a soapy foam appearance resulting in a tendency of the froth layer to collapse rapidly after its dispensing in the cup.
Another usual shortcoming more particularly, applicable for the preparation of cappuccino type beverages in automated dispensing apparatuses is that the milk froth and the liquid coffee phase slightly mix together during dispensing because of gravity and the dispensing flow rates. This results in an unpleasant, spotted brown dark coloration of the milk froth due to interstitial coffee present in the froth matrix.
Attempts have been made to overcome the problems encountered in the preparation of hot frothy beverages of the kind of cappuccino with automated dispensing apparatuses. One particular solution implemented is to inject water steam or pressurized air into a separate portion of milk to froth that portion individually and then pour it directly onto the coffee surface in the cup. But this does not compensate for the collapsing of the foam and it also often requires a separate container or bowl where to froth a part of the milk and thus increasing the number of elements in the dispensing apparatus. Another type of solution developed has been to design new dispensing devices to emulsify milk directly in a mixing chamber formed in a dispensing pipe while or prior to dispensing. The frothing of the milk is achieved thanks to mixing of pressurized gas and milk together in the mixing chamber and release of the frothed milk at the outlet of the mixing chamber located downstream relative to it. But in this case, the pressure of the gas in the mixing chamber causes high outflow rate of the frothed milk from the chamber and thus mixing of the froth with the coffee beverage in the cup resulting in the unpleasant brown color of the froth. This may also complicate hygienic cleaning of the pipe and mix chamber without leakage of cleaning product or fluid from the pipe.